29'ers typically climb better and handle small bumps better. They track better over rough terrain due to the larger wheel. However, they dont corner as easily and are a little more cumbersome than 26" wheels. I have several bikes both 26" and 29". I like each for different reasons. If you just riding singletrack cross country and not riding downhill or freeriding, 29'ers are a good choice.
_________________________
Climb the Mountains and get their good tidings...
-John Muir